Polymer electrolyte fuel cell

ABSTRACT

The polymer electrolyte fuel cell of the present invention is equipped with a cell having an MEA having a hydrogen ion-conducting polymer electrolyte membrane and an anode and a cathode sandwiching the polymer electrolyte membrane; a platelike anode-side separator positioned on one side of the MEA so that the front surface thereof contacts the anode, with fuel gas passages through which fuel gas flows being formed in the front surface; and a platelike cathode-side separator positioned on the other side of the MEA so that the front surface thereof contacts the cathode, with oxidizing gas passages through which oxidizing gas flows being formed in the front surface; a cell stack in which a plurality of said cells is stacked; and a cooling water flow passage, through which cooling water flows, formed on at least the rear surface of one from among the anode-side separator and the cathode-side separator of at least a prescribed cell in said cell stack; where said fuel gas, oxidizing gas, and cooling water flow through said fuel gas passage, oxidizing gas passage, and cooling water passage, respectively, in a manner not running counter to gravity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to portable power sources, power sourcesfor electric automobiles, fuel cells for use in household cogenerationsystems and the like, and in particular, to a polymer electrolyte fuelcell employing a polymer electrolyte.

2. Description of Related Technology

In fuel cells employing polymer electrolytes, a fuel gas containinghydrogen is electrochemically reacted with an oxidizing gas containingoxygen, such as air, to simultaneously generate power and heat. Thisfuel cell is basically comprised of a polymer electrolyte membraneselectively transferring hydrogen ions and a pair of electrodes formedon either side of the polymer electrolyte membrane, that is, an anodeand a cathode. The electrodes are comprised of a catalyst layer, formedon the surface of the polymer electrolyte membrane, that is comprisedchiefly of carbon powder supported on a platinum group metal catalyst,and a gas diffusion layer, having both gas permeability andelectron-conducting capability, formed on the outer surface of thecatalyst layer.

To prevent oxidizing gas and fuel gas fed to the electrodes from leakingto the exterior and to prevent mixing of the two gases, the electrodesare formed on the two surfaces of portions outside the rim portion ofthe polymer electrolyte membrane and gas seals and gaskets arepositioned in a manner surrounding the electrodes on the rim portions ofthe polymer electrolyte membrane. These gas seals and gaskets areintegrated and preassembled with the electrodes and polymer electrolytemembrane. This integrated and preassembly combination is hereinafterreferred to as a membrane electrode assembly (“MEA”). The MEA ismechanically secured and electrically conductive separators forelectrically connecting adjacent MEAs in series are provided on bothsides thereof. Gas passages for feeding reaction gas to the electrodesurface and carrying off water that is generated and excess gas areformed on the portions where the separators contact the MEA. The gaspassages can be provided separately from the separators, but the methodof forming grooves serving as gas passages on the outer surface of theseparator is generally adopted.

The supplying of reaction gas to the gas passages and the discharging ofwater produced and reaction gas from the gas passages are conducted byproviding a through-hole known as a manifold hole in the separator,connecting the gas passage inlet and outlet to the manifold hole, anddistributing reaction gas to the various gas passages through themanifold hole. Since the fuel cell generates heat during operation,maintaining the cell at proper temperature requires cooling with acooling fluid, such as cooling water, or the like. Normally, a coolingmember through which cooling water flows is provided for every one tothree cells. The MEA, separator, and cooling member are stacked inalternating fashion to achieve 10 to 200 cell layers, after which theyare sandwiched between terminal plates through current collecting platesand insulating plates, and then secured at each end with fastening rodsinto a common stacked cell structure. While not wishing to be bound to aspecific construction of a cell stack, a typical construction can befound in U.S. Published Application US 2002/01456601 and U.S. Pat. No.6,413,664, both herein incorporated by reference.

Perfluorosulfonic acid-based materials have come to be used in thepolymer electrolyte membranes of such cells. It is normally necessary tomoisten the fuel gas and oxidizing gas and feed them to the cell for thepolymer electrolyte membrane to develop ion conductivity in amoisture-comprising state. On the cathode side, water is generated insome reactions. Thus, when a gas that has been moistened to increase thedew point to above the working temperature of the cell is supplied,there is sometimes a problem in that condensation forms in the gaspassages in the cell and within the electrodes and water blockageoccurs, rendering cell performance unstable and decreasing performance.This phenomenon of decreased cell performance and unstable operation dueto excessive wetting is generally called “flooding”. Additionally, whenthe fuel cell is being used in a power generating system, it isnecessary to systemize the wetting of feed gas and the like. To simplifythe system and enhance system efficiency, it is desirable to at leastslightly reduce the dew point of the wetted gas that is supplied.

From the perspectives of preventing flooding, enhancing systemefficiency, and simplifying the system set forth above, the feed gas isusually moistened so that its dew point is slightly lower than the celltemperature before being supplied.

However, it is also necessary to increase the ion conductivity of thepolymer electrolyte membrane to increase the performance of the cell.Thus, it is desirable to moisten the fuel gas and feed it at a relativehumidity of near 100 percent, or even at 100 percent humidity and above.Further, from the perspective of the durability of the polymerelectrolyte membrane, as well, the supplying of feed gas with a highmoisture content is known to be desirable. However, when supplying moistgas at, or close to 100 percent relative humidity, the above-describedflooding becomes a problem. That is, in operation of prior cells, thehumidity of the feed gas cannot be adjusted accurately and preciselyenough to inevitably prevent flooding.

A method of increasing the flow rate of feed gas through the separatorpassage portion to blow out water that has condensed is known to be aneffective way to remove condensation to avoid flooding. However, it thenbecomes necessary to feed the gas at high pressure to increase the feedgas flow rate in order to blow out the condensed water, requiring anextreme increase in the auxiliary power of the blower or compressorsupplying the gas when using the cells in a systemized environmentthereby tending to result in deterioration of system efficiency.Further, when flooding occurs on the anode side, flow of fuel gas tendsto be blocked or diminished, which ends up being fatal to the fuel cell.This is because load current is forcefully removed in a state where theflow of fuel gas is inadequate, and the carbon supporting the catalystof the anode ends up reacting with water in the atmosphere to produceelectrons and protons in a state without fuel. As a result, dissolutionof carbon in the catalyst layer permanently damages the catalyst layerof the anode.

Furthermore, in systems in which stacked cells are mounted, commercialconsiderations dictate that the cell be able to operate not only underrated output conditions, but also operate under low loads when output isreduced based on power demand. Maintaining efficiency under low loadoperation requires that the use rates of fuel gas and oxidizing gas bemade identical to rated operation conditions. That is, when the load isreduced by ½ relative to rated operation, for example, if the flow ratesof the fuel gas and oxidizing gas are not decreased by about ½, excessfuel gas and oxidizing gas are consumed, causing power generationefficiency to drop. However, when the gas use rate is preset and lowload operation is conducted, there are problems in that the gas flowrate in the gas passages decreases, condensation water and generatedwater cannot be discharged from the separator, the above-describedflooding occurs, cell performance decreases, and performance becomesunstable.

It is also known that condensed water and generated water collect inportions of the gas passage where the flow runs against gravity if suchportions are present, tending to cause flooding. As a countermeasure,methods of making the oxidizing gas or fuel gas flow in directions thatdo not run against gravity have been proposed (Japanese PatentApplication Publication Nos. Hei 11-233126 and 2001-068131, bothincorporated herein by reference). Based on these methods, the oxidizinggas or fuel gas is made to flow in directions that do not run counter togravity, thereby permitting smooth discharge of condensed water andgenerated water and inhibiting flooding. However, this proposal does notaddress the drying out of the polymer electrolyte membrane necessary todevelop ion conductivity.

SUMMARY OF THE INVENTION

Generally, as the oxidizing gas and fuel gas flow from the cell inlet tothe outlet, the quantity of gas decreases and the amount of watergenerated increases the farther downstream the gas moves, so therelative humidity increases. Further, when 100 percent relative humidityis exceeded, the amount of moisture becoming condensation increases. Bycontrast, the cooling water increases in temperature from a minimumtemperature at the inlet to the cell to a maximum temperature as itmoves toward the outlet. As stated above, feed gas must be fed into thecell in a moist state at, or close to 100 percent relative humidity.Normally, the cooling water flows to the main surface over which thereaction gas of the separator flows and the main surface on the reverseside, thereby cooling the heat-generating electrodes through theseparator. Here, if the cooling water is made to flow in the oppositedirection to the flow of the reaction gas, it becomes necessary tosupply reaction gas that has been moistened to 100 percent relativehumidity relative to the high-temperature cooling water. Further, thislarge quantity of moistened gas that is supplied all becomescondensation water at the reaction gas downstream portion where thetemperature of the cooling water is low, so flooding due to waterblockage, and the like, tends to occur. Further, in actual cogenerationsystems, when cooling water is employed to moisten the feed gas, it isimpossible to raise the moistening temperature to the same temperatureas the outlet temperature of the cooling water. As a result, since thereaction gas cannot be supplied at a relative humidity of 100 percent,there is a problem in that the polymer electrolyte membrane tends tobecome dry in spots near the gas inlet and durability deteriorates.

Further, if the cooling water is fed to the stack from the top in thedirection of gravity, flowing downward, the cooling water branches undergravity into each cooling water flow passage from the inlet manifoldhole of the cooling water, causing larger quantities of cooling water toflow to cells closer to the cooling water inlet pipe of the manifoldhole and resulting in uneven distribution of cooling water. Inparticular, since the amount of heat generated by the power generationreaction diminishes during partial load operation, it is necessary toreduce the flow rate of cooling water to maintain a constant celltemperature. This reduction also creates the problem of uneven coolingwater distribution.

The present invention has for its object to solve the above-statedproblems. To achieve this object, the polymer electrolyte fuel cell ofthe present invention is equipped with a cell comprising an MEA having ahydrogen ion-conducting polymer electrolyte membrane and an anode and acathode sandwiching the polymer electrolyte membrane, a platelikeanode-side separator the front surface of which is positioned on oneside of the MEA so as to be in contact with the anode, with fuel gaspassages through which fuel gas flows being formed in this frontsurface, and a platelike cathode-side separator the front surface ofwhich is positioned on the other side of the MEA so as to be in contactwith the cathode, with oxidizing gas passages through which oxidizinggas flows being formed in this front surface; a cell stack in whichmultiple cells of this type are stacked; and cooling water flowpassages, through which cooling water flows, formed on at least the backsurface of either the anode side separator or the cathode side separatorof at least a prescribed cell of the cell stack. The fuel gas, oxidizinggas, and cooling water are made to flow through the fuel gas passages,oxidizing gas passages, and cooling water passages, respectively,without running counter to gravity. However, there may be portions inthe manifold where the fuel gas, oxidizing gas, or cooling water flowscounter to gravity.

In one embodiment, at least one of the fuel gas flow passages, oxidizinggas flow passages, and cooling water flow passages may also be formed torun downstream either horizontally or with a downward gradient.

In another embodiment, at least one from among the fuel gas flowpassages, oxidizing gas flow passages, and cooling water flow passagesmay be essentially configured of horizontal and vertical portions. In analternative embodiment, the fuel gas flow passages, oxidizing gas flowpass and cooling water flow passages comprise downwardly sloping andvertical portions.

The upstream portion of the oxidizing gas flow passage may be positionedin the vicinity of the inlet of the cooling water flow passage in thecathode-side separator.

The upstream portion of the fuel gas flow passage may be positioned inthe vicinity of the inlet of the cooling water flow passage in theanode-side separator.

The cooling water flow passages and oxidizing gas flow passages may beformed so as to be aligned approximately throughout as viewed in thedirection of thickness in the cathode-side separator.

In the anode-side separator or cathode-side separator, an inlet manifoldhole feeding cooling water to the cooling water passages may be providedso as to run through the separator in the direction of its thickness andto have a constriction comprised of locally narrowing portions in theopposing internal circumference surfaces, with a first portion that ispositioned on one side of the constriction and communicates to a coolingwater supply pipe and a second portion that is positioned on the otherside of the constriction and communicates to the cooling water flowpassage.

In the anode-side separator or cathode-side separator, an inlet manifoldhole feeding cooling water to the cooling water passages may be providedso as to run through the separator in the direction of its thickness andto have a step running in a circumferential direction on the lowerportion of the inner circumference surface, with a first portion that ispositioned beneath the step and communicates to a cooling water supplypipe and a second portion that is positioned above the step andcommunicates to the cooling water flow passage.

The above object and additional objects, characteristics, and advantageswill be made clear from a detailed description of suitableimplementation modes below with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of the cathode-side separator employed in thefuel cell of a first mode of implementing the present invention.

FIG. 2 is a rear view of the same cathode-side separator.

FIG. 3 is a front view of the anode-side separator employed in the fuelcell of the first mode of implementing the present invention.

FIG. 4 is a rear view of the same anode-side separator.

FIG. 5 is a rear view of an anode-side separator employed in the fuelcell of a second mode of implementing the present invention.

FIG. 6 is a rear view of an anode-side separator employed in the fuelcell of a third mode of implementing the present invention.

FIG. 7 is a graph of the current-voltage characteristics of the fuelcells of Example 1 and Comparative Example 1 of the present invention.

FIG. 8 is a graph showing the relation between cell number and cellvoltage in the fuel cells of Examples 1 and 2 of the present invention.

FIG. 9 is a graph showing the relation between the cell number and cellvoltage after a durability test of the fuel cells of Examples 1 and 2 ofthe present invention.

FIG. 10 is a graph showing the relation between the cell number and cellvoltage in the fuel cells of Examples 2 and 3 of the present invention.

FIG. 11 is a graph showing the relation between the cell number and cellvoltage after a durability test of the fuel cells of Examples 2 and 3.of the present invention.

FIG. 12 is a perspective view of the approximate configuration of thepolymer electrolyte fuel cell of the first mode of implementing thepresent invention.

FIG. 13 is a sectional view along section lines XIII-XIII of FIG. 12.

FIG. 13A is a sectional, enlarged view along lines A-A of FIG. 13.

FIG. 14 is a front side view of the cathode-side separative in analternative embodiment to FIG. 1.

FIG. 15 is a front view of the anode-side separator in an alternativeembodiment of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

1. Concept of the Invention

The concept of the present invention will be described first. Thepresent inventors discovered that by directing the flow passages of atleast one of the fuel gas, the oxidizing gas and the coolant fluid,preferably at least two flows, most preferably all flows in a directionthat does not run counter to gravity the flows of oxidizing gas, fuelgas, and cooling water that occur in a surface parallel to the surfaceon which the electrodes extend, it was possible to promote the smoothdischarge of condensation water, improve toughness with respect toflooding, prevent drying of the electrolyte membrane in the gas inletportion, and improve the durability of the fuel cells. A first aspect ofthe present invention was based on this knowledge.

Further, a second aspect of the present invention ensures the gooddistribution of cooling water by providing a constriction or step in thecooling water inlet manifold hole.

2. Detailed Description of the Embodiments of the Invention

To enhance the commercial properties of fuel cell power generatingsystems, the load of the fuel cell can desirably be varied based onpower demand without a drop in power generation efficiency. To that end,when increasing the load relative to the rated output, operation must beconducted with the flow outputs of fuel gas and oxidizing gascorrespondingly increased, and when decreasing the load relative to therated output, operation must be conducted with the flow rates of thefuel gas and oxidizing gas correspondingly reduced. Normally, the gaspassages provided in the electrically conductive separator employed inthe fuel cell are designed to yield the gas flow speeds best suited tothe rated output. Accordingly, when increasing the power load, the gasflow speed in the passages increases as the gas flow rate increases, andwhen decreasing the power load, the gas flow speed in the passagesdecreases as the gas flow rate decreases. Since the pressure loss of thefeed gas increases when increasing the gas flow speed in the passages,power generation efficiency drops somewhat due to increased auxiliarymotor power. However, since the gas flow speed in the passagesincreases, it becomes possible to efficiently remove condensation waterand generated water in the gas passages of the separator and floodingdoes not occur.

However, when decreasing the power load, the gas flow speed in thepassages decreases as the gas flow rate decreases. When the gas flowspeed in the passages decreases, it becomes difficult to efficientlyremove condensation water and generated water from the gas passages ofthe separator based on gas flow speed and flooding occurs. At suchtimes, although the power load has been reduced, the flow rate of thefeed gas must also be reduced, the relative proportion of auxiliarypower relative to power output increases, and the power generatingefficiency of the generating system as a whole decreases. Further, it isnecessary at such times to change the cooling water flow rate to matchthe change in power load to keep the temperature of the fuel cellsconstant. In particular, when decreasing the flow rate of cooling waterduring a low load, the uniform distribution of cooling water is lost.

The present invention causes at least one of, preferably at least twoof, and most preferably all of the oxidizing gas passages and fuel gaspassages, to run in directions that are not counter to gravity, therebypromoting the smooth discharge of condensation water to preventflooding, while simultaneously supplying cooling fluid passagesproximate the inlets of the fuel gas and/or oxidizing gas passageseliminating drying out of the electrolyte membrane in the gas inletportion to enhance durability. For example, when the flow speed of gasbecomes ¼ when the ratio of the maximum load generation output to theminimum load generation output is set at 4 to 1, the gas use rate ismade constant, and the gas flow is decreased. In a conventionalseparator, when the gas flow speed decreases, condensation water cannotbe discharged against gravity and flooding occurs. By contrast, in oneembodiment of the present invention, since the oxidizing gas and thefuel gas are both constantly made to flow in a direction not runningcounter to gravity, it was discovered that the smooth discharge ofcondensation water became possible and flooding did not occur. Further,it was discovered that drying out of the electrolyte membrane could beeliminated and durability thus improved by matching the gas inlet portwith the lowest relative humidity with the inlet port of the coolingwater as viewed in the direction of thickness of the separator.

Further, in another embodiment according to the invention, it was foundthat by providing a constriction in the cooling water inlet manifoldhole, it was possible to improve the uniformity of cooling waterdistribution in the course of distributing cooling water supplied to thecell stack to multiple cooling water passages in the cell stack. It wasfurther discovered that by positioning the inlet of each of the passagesfor distribution of cooling water from the cooling water inlet manifoldhole to the various passages higher in the direction of gravity than theposition at which the cooling water was supplied to the cooling watermanifold hole, it was possible to ensure uniform distribution even whenthe cooling water flow rate had been reduced, thereby achieving stableoperation.

The various modes of implementing the present invention are describedbelow with reference to the figures.

Implementation Mode 1

FIG. 12 is a perspective view of the schematic configuration of apolymer electrolyte fuel cell (referred to simply as a “fuel cell”hereinafter) relating to Implementation Mode 1 of the present invention.FIG. 13 is a sectional view along section line XIII-XIII of FIG. 12.FIG. 13A is a section enlarged view along A-A of FIG. 13.

In FIG. 12, the vertical direction in the fuel cell is denoted as thevertical direction in the figure. The same holds true for FIGS. 1through 6, described further below.

As shown in FIG. 12, the fuel cell of the present implementation modehas a cell stack 1.

Cell stack 1 comprises a cell stack body 101 in which cells 2, 2′, 2″,2″′, etc., with an overall platelike shape are stacked in the directionof their thickness, first and second end plates (3A, 3B) positioned onthe two ends of cell stack body 101, and fasteners (not shown),fastening cell stack body 2 and first and second end plates 3A and 3B inthe stacking direction of cell 2. Further, current collecting terminals(not shown) are positioned on first end plate 3A and second end plate3B.

Platelike cells 2 extend parallel to the vertical. Accordingly, thestacking direction of cells 2, 2′, 2″, 2″′, etc. is horizontal.

Oxidizing gas supply manifold 4 is formed in the top part of one of thesides (referred to as the “side 1 portion” hereinafter) of cell stackbody 101 so as to run through cell stack body 101 in the stackingdirection. One end of oxidizing gas supply manifold 4 communicates withthe through-hole formed in first end plate 3A, with oxidizing gas supplypipe 51 being connected to this through-hole. The other end of oxidizinggas supply manifold 4 is sealed off by end plate 3B. Further, anoxidizing gas discharge manifold 7 is formed in the lower part of theother side portion (referred to as the “side 2 portion” hereinafter) ofcell stack body 101 so as to run through cell stack body 101 in thestacking direction. One end (i.e., the discharge end) of oxidizing gassupply manifold 7 is sealed off by first end plate 3A. The other end ofoxidizing gas discharge manifold 7 communicates with the through-holeformed in second end plate 3B, with oxidizing gas discharge pipe 52being connected to this through-hole.

A fuel gas supply manifold 5 is formed in the upper part of the side 2portion of cell stack body 101 so as to run through cell stack body 101in the stacking direction. One end of fuel gas supply manifold 5communicates with a through-hole formed in first end plate 3A, with fuelgas supply pipe 53 being connected to this through-hole. The other endof fuel gas supply manifold 5 is sealed off by second end plate 3B.Further, a fuel gas discharge manifold 6 is formed in the lower part ofthe side 1 portion of cell stack body 101 so as to run through cellstack body 101 in the stacking direction. One end of fuel gas dischargemanifold 6 is sealed off by first end plate 3A. The other end of fuelgas supply manifold 5 communicates with a through-hole formed in secondend plate 3B, with fuel gas discharge pipe 54 being connected to thisthrough-hole.

A cooling water supply manifold 8 is connected to the inside of the toppart of oxidizing gas supply manifold 4 so as to run through cell stackbody 101 in the stacking direction. One end of cooling water supplymanifold 8 communicates with a through-hole formed in first end cap 3A,with a cooling water supply pipe 30 being connected to thisthrough-hole. The other end of cooling water supply manifold 8 is sealedby second end plate 3B. Further, a cooling water discharge manifold 9 isformed on the inside of the lower part of oxidizing gas dischargemanifold 7 so as to run through cell stack body 101 in the stackingdirection. One end of cooling water discharge manifold 9 is sealed offby first end plate 3A. The other end of cooling water discharge manifold9 communicates with a through-hole formed in second end plate 3B, with acooling water discharge pipe 31 being connected to this through-hole.Cooling water supply manifold 8 and cooling water discharge manifold 9have cross-sections in the form of long holes or slots (a shape in whichtwo opposing straight lines have been replaced with semicircles on twosides) running in the horizontal direction.

As shown in FIG. 13, cell 2 is comprised of a platelike MEA 43, and acathode-side separator 10 and an anode-side separator 20 positioned incontact with the two main surfaces of MEA 43. Cells 2 are stacked sothat in adjacent cells 2 and 2′ (FIG. 13), the back side of thecathode-side separator 10 of one cell 2 contacts the back side of theanode-side separator 20 of the other cell 2′. MEA 43, cathode-sideseparator 10, and anode-side separator 20 are formed in a single shape(here, rectangles) of the same size. An oxidizing agent inlet manifoldhole, oxidizing agent outlet manifold hole, fuel inlet manifold hole,fuel outlet manifold hole, cooling water inlet manifold hole, andcooling water outlet manifold hole are formed in MEA 43, cathode-sideseparator 10, and anode-side separator 20 at prescribed mutuallycorresponding spots so that they run in the direction of thickness ofthese parts. The oxidizing agent inlet manifold holes, oxidizing agentoutlet manifold holes, fuel inlet manifold holes, fuel outlet manifoldholes, cooling water inlet manifold holes, and cooling water outletmanifold holes of all of the MEAs 43, cathode-side separators 10, andanode-side separators 20 are linked in all of cells 2, forming oxidizingagent supply manifold 4, oxidizing agent discharge manifold 7, fuelsupply manifold 5, fuel discharge manifold 6, cooling water supplymanifold 8, and cooling water discharge manifold 7, respectively.

Oxidizing agent gas passage 17 and cooling water passage 19 are formedin the front surface and back surface, respectively, of cathode-sideseparator 10. As described further below, oxidizing agent gas passage 17is formed so as to connect the oxidizing agent gas inlet manifold holeand the oxidizing agent gas outlet manifold. As described further below,cooling water passage 19 is formed so as to connect the cooling waterinlet manifold hole and the cooling water outlet manifold hole.Cathode-side separator 10 is positioned with its front surface incontact with MEA 43.

Fuel gas passage 28 and cooling water passage 29 are formed in the frontsurface and back surface, respectively, of anode-side separator 20. Asdescribed further below, fuel gas passage 19 is formed so as to connectthe fuel gas inlet manifold hole and the fuel gas outlet manifold hole.As described further below, cooling water passage 29 is formed so as toconnect the cooling water inlet manifold hole and the cooling wateroutlet manifold hole. Anode-side separator 20 is positioned with itsfront surface in contact with MEA 43.

Passages 17, 19, and 28 are comprised of grooves formed in the mainsurfaces of cathode-side separator 10 and anode-side separator 20. InFIG. 13, passages 17, 19, 28, and 29 are each comprised of two passages,but can also be comprised of multiple passages.

The cooling water passage 19 of cathode-side separator 10 and thecooling water passage 29 of adjacent anode-side separator 20 are formedso as to match up (i.e., connect) when cells 2, 2′ (FIG. 13) arestacked, the two forming a single cooling water passage.

O-ring receiving grooves are formed on the back side of cathode-sideseparator 10 and on the back side of anode-side separator 20 so as tosurround the cooling water inlet manifold hole, cooling water outletmanifold hole, cooling water passage, oxidizing agent inlet manifoldhole, oxidizing agent outlet manifold hole, fuel inlet manifold hole,and fuel outlet manifold hole, respectively, and O-rings 47 arepositioned in those grooves. Thus, the manifold holes are sealed offfrom each other.

MEA 43 comprises a polymer electrolyte membrane 41, a cathode 42A, ananode 42B, and a pair of gaskets 46. Cathode 42A and anode 42B areformed on the two surfaces of portions outside the rim portion ofpolymer electrolyte membrane 41, with gaskets 46 being positioned on thetwo surfaces of the rim portions of polymer electrolyte membrane 41 soas to surround cathode 42A and anode 42B. The pair of gaskets 46,cathode 42A, anode 42B, and polymer electrolyte membrane 41 areintegrated.

Cathode 42A, anode 42B, the area in which oxidizing agent gas passage 17is formed and the area in which cooling water passage 19 is formed incathode-side separator 10, and the area in which fuel gas passage 28 isformed and the area in which cooling water passage 29 is formed inanode-side separator 20 are positioned so as to essentially line upoverall when viewed from the stacking direction of cell 2, 2′, 2″, etc.

The cathode-side separator and the anode-side separator will bedescribed in detail next.

FIG. 1 is a front view of the cathode-side separator. FIG. 2 is a rearview of the same. FIG. 3 is a front view of the anode-side separator.And FIG. 4 is a rear view of the same.

As shown in FIG. 1, cathode-side separator 10 comprises an oxidizing gasinlet manifold hole 11 and outlet manifold hole 13, a fuel gas inletmanifold hole 12 and outlet manifold hole 14, and a cooling water inletmanifold hole 15 and outlet manifold hole 16. Separator 10 furthercomprises a gas passage 17 connecting manifold holes 11 and 13 on thesurface facing the cathode, and a passage 19 connecting cooling watermanifold holes 15 and 16 on the rear side.

In FIG. 1, oxidizing gas inlet manifold hole 11 is provided in the toppart of one side (the left side in the figure: the “first side portion”hereinafter) of separator 10, and outlet manifold hole 13 is provided inthe bottom part of the other side (the right side in the figure: the“second side portion” hereinafter) of separator 10. Fuel gas inletmanifold hole 12 is provided in the top part of the second side portionof separator 10 and outlet manifold hole 14 is provided in the bottompart of the first side portion of separator 10. Cooling water inletmanifold hole 15 is provided on the inside of the top part of oxidizinggas inlet manifold hole 11 and outlet manifold hole 16 is provided onthe inside of the bottom part of oxidizing gas outlet manifold hole 13.Cooling water manifold holes 15 and 16 are formed as long slots in thehorizontal direction.

Oxidizing gas passage 17 is comprised of two passages in the presentimplementation mode. Naturally, it could be comprised of any number ofpassages. In this embodiment, each passage is essentially comprised ofhorizontal portions 17 a extending in the horizontal direction andvertical portions 17 b extending in the vertical direction.Specifically, each of the passages of oxidizing gas passage 17 runshorizontally from the top part of oxidizing gas inlet manifold hole 11to the second side portion of separator 10, downward for some distance,horizontally from there to the first side portion of separator 10, andfrom there downward. From there, the above extension pattern repeatstwice, and from that point, runs horizontally, reaching the lower partof oxidizing gas outlet manifold hole 13. The horizontally runningportions of each passage form horizontal parts 17 a, and the downwardrunning portions form vertical parts 17 b. In this manner, in oxidizinggas passage 17, the oxidizing gas weaves back and forth, alternatelypassing through horizontal parts 17 a and vertical parts 17 b whileflowing in a manner that does not run counter to gravity. As a result,flooding is prevented.

The individual passages are comprised here of horizontal parts 17 a andvertical parts 17 b. However, they can also be configured to behorizontal and/or downward sloping, optionally including verticalportions, in the direction of the gas flow. However, having theindividual passages comprise horizontal parts 17 a and vertical parts 17b permits the formation of a highly dense oxidizing gas passage 17.

In an alternative embodiment as illustrated in FIG. 14, the passagescomprise downwardly sloping portions and vertical portions, none ofwhich run counter to gravity. (In this embodiment, FIG. 14 is similarlynumbered to analogous structure in FIG. 1, but the use of prime (′)numbers are employed to show the downwardly sloping portions.) In thisembodiment, we have shown only one of the two passages comprisingdownwardly sloping positions for purposes of illustration in FIG. 14.However, it is to be understood that this illustration is exemplary onlyand not limiting as one, two or all of the passageways may be downwardlysloping and be within the teachings of the invention.

In FIG. 2, cooling water passage 19 is comprised of two passages. Eachpassage is essentially comprised of horizontally running horizontalparts 19 a and vertically running vertical parts 19 b. Specifically,each of the passages of cooling water passage 19 runs downward a certaindistance from the end portion near oxidizing gas inlet manifold hole 11of cooling water inlet manifold hole 15. From there, it runshorizontally to the second side portion of separator 10 (the left sidein the figure). From there, it runs downward a certain distance, andthen extends horizontally to the first side portion (the right side inthe picture). From there, the above extension pattern repeats twice, andfrom the arrival point, runs downward to reach the end portion close tooxidizing gas outlet manifold hole 13 of cooling water outlet manifoldhole 16. The horizontally running portions of each passage formhorizontal parts 19 a and the vertically running portions form verticalportions 19 b. Thus, in cooling water passage 19, the cooling waterwinds back and forth, passing alternately through horizontal parts 19 aand vertical parts 19 b while flowing in a manner that does not runagainst gravity.

The following points are important here. Cooling water inlet manifoldhole 15 and oxidizing gas inlet manifold hole 11 are positioned in closeproximity. Cooling water outlet manifold hole 16 and oxidizing gasoutlet manifold hole 13 are positioned in close proximity. Viewed fromthe direction of thickness of separator 10, cooling water passage 18 isformed in such a manner as to essentially align with oxidizing gaspassage 17. As a result, the cooling water and the oxidizing gas flow inessentially the same direction on either side of separator 10; In such aconfiguration, the oxidizing gas inlet portion where the relativehumidity is the lowest roughly corresponds to the cooling water inletportion when viewed from the direction of thickness of separator 10.Thus, drying out of the polymer electrolyte membrane can be eliminatedand the durability of the polymer electrolyte membrane can be improved.

Here, each passage is essentially comprised of horizontal parts 19 a andvertical parts 19 b. Each passage can also be formed to be horizontal orhave a downward gradient in the direction of flow of the cooling water.However, having the individual passages comprise horizontal parts 19 aand vertical parts 19 b permits the formation of a highly dense coolingwater passage 19.

Anode-side separator 20 comprises oxidizing gas inlet manifold hole 21and outlet manifold hole 23, fuel gas inlet manifold hole 22 and outletmanifold hole 24, and cooling water inlet manifold hole 25 and outletmanifold hole 26. Separator 20 further comprises gas passage 28connecting manifold holes 22 and 24 on the surface facing the anode, andpassage 29 connecting cooling water manifold holes 25 and 26 on the backsurface.

In FIG. 3, oxidizing gas inlet manifold hole 21 is provided in the upperpart of one side (the right side in the figure: referred to as the“first side portion” hereinafter) of separator 20, and outlet manifoldhole 23 is provided in the lower part of the other side (the left sidein the figure: referred to as the “second side portion” hereinafter) ofseparator 20. Fuel gas inlet manifold hole 22 is provided in the upperpart of the second side portion of separator 20, and outlet manifoldhole 24 is provided in the lower part of the first side portion ofseparator 20. Cooling water inlet manifold hole 25 is provided on theinside of the upper part of oxidizing gas inlet manifold hole 21, andoutlet manifold hole 26 is provided on the inside of the lower part ofoxidizing gas outlet manifold hole 23. Cooling water manifold holes 25and 26 are formed as long horizontally running slots.

Fuel gas passage 28 is comprised of two passages in the presentimplementation mode. Each passage is essentially comprised of horizontalportions 28 a running horizontally and vertical portions 28 b runningvertically. Specifically, both of the passages of fuel gas passage 28run from the top portion of fuel gas inlet manifold hole 22 horizontallyto the first side portion of separator 20, extending downward from therefor a certain distance, after which they run horizontally to the secondside portion of separator 20, and then downward for a certain distance.From there, the above extension pattern is repeated twice. From thearrival point, they run horizontally, reaching the lower portion of fuelgas outlet manifold hole 24. The portions of each of the passagesrunning horizontally constitute horizontal portions 28 a and thoseextending downward constitute vertical portions 28 b. Thus, in fuel gaspassage 28, the fuel gas winds back and forth, flowing alternatelythrough horizontal portions 28 a and vertical portions 28 b in a mannerthat does not run counter to gravity. As a result, flooding isprevented.

Here, the passages are essentially comprised of horizontal portions 28 aand vertical portions 28 b. However, it suffices for them to be madehorizontal or have a downward incline (including vertical) in thedirection of gas flow. However, having the individual passages becomprised of horizontal parts 28 a and vertical parts 28 b permits theformation of a highly dense fuel gas passage 28.

As shown in an alternative embodiment to FIG. 3 as shown in FIG. 15, thepassages are shown in a downward incline with like numbers being giventhe same numerals as in FIG. 3 with analogous elements marked with aprime (′). As with the description of FIG. 14, only one passage is shownwith a downward gradient, but it is to be understood that, as in FIG.14, such teaching is exemplary only and non-limiting as one, two or allpassages may possess a downward gradient.

In FIG. 4, cooling water passage 29 is formed as the mirror image of thecooling water passage 19 formed on the back surface of cathode separator10 in FIG. 2. That is, each of the passages is essentially comprised ofhorizontally extending horizontal portions 29 a and vertically extendingvertical portions 29 b. Specifically, the individual passages of coolingwater passage 29 extend downward for some distance from the end portion,near oxidizing gas inlet manifold hole 21, of cooling water inletmanifold hole 25. From there, they run horizontally to the second sideportion (the right side in the figure) of separator 20, downward forsome distance, and then horizontally to the first side portion (the leftside in the figure). From there, this extension pattern is repeatedtwice. From the arrival point, they extend downward to the end, nearoxidizing gas outlet manifold hole 23, of cooling water outlet manifoldhole 26. The portions of the passages running horizontally constitutehorizontal portions 29 a and the portions running downward constitutevertical portions 29 b. Thus, in cooling water passage 29, the coolingwater winds back and forth, flowing alternately through horizontalportions 29 a and vertical portions 29 b while flowing in a manner thatdoes not run counter to gravity.

Here it is important to note the following points. Both cooling waterinlet manifold hole 25 and fuel gas inlet manifold hole 22 are providedin the top portion of separator 20. Both cooling water outlet manifoldhole 26 and fuel gas outlet manifold hole 24 are provided in the bottomportion of separator 20. When viewed in the direction of thickness ofseparator 20, cooling water passage 29 is formed to be essentiallyaligned with fuel gas passage 28. As a result, the cooling water and theoxidizing gas flow in mutually opposed directions on either side ofseparator 20 in the horizontal direction, but in the vertical direction,they flow in the same overall direction from top to bottom. Such aconfiguration positions the upstream portion of fuel gas passage 28,where the relative humidity is the lowest, above the spot where thecooling water inlet portion is positioned, where the temperature is thelowest, in the vertical direction of separator 20. This helps preventdrying out of the polymer electrolyte, and thus improves the durabilityof the polymer electrolyte membrane.

Here, the individual passages are essentially comprised of horizontalportions 29 a and vertical portions 29 b. However, it suffices for thepassages to run horizontally or have a downward gradient in thedirection of flow of the cooling water. Configuring the passages withhorizontal portions 29 a and vertical portions 29 b permits the formingof a highly dense cooling water passage 29.

As previously stated, the cell is comprised of an MEA sandwiched betweenthe above-described cathode-side separator 10 and anode-side separator20. Accordingly, adjacent cells are laid out so that the cooling waterpassages 19 and 29 of the cathode-side separator 10 and anode-sideseparator 20 line up to form cooling members. When a cooling member isprovided in each of multiple cells, instead of the above-describedmultiple separators, a single separator, one surface of which functionsas a cathode-side separator and the other surface of which functions asan anode-side separator, can be suitably employed.

The fuel gas, oxidizing gas, and cooling water flow operations of a fuelcell configured as set forth above will be described next.

In FIGS. 1 through 6, 12, and 14, fuel gas passes through a fuel gassupply pipe 43 and is fed into fuel gas supply manifold 5 of cell stack1. The fuel gas that is supplied flows from fuel gas supply manifold 5to the inlet manifold hole 22 of each cell 2 over fuel gas passage 28.During this time, it reacts with oxidizing gas through the anode,polymer electrolyte membrane, and cathode and is consumed. Unconsumedfuel gas is caused to flow out from outlet manifold hole 24 to fuel gasdischarge manifold 6 as off gas, and is discharged through fuel gasdischarge pipe 44 from cell stack 1.

Oxidizing gas passes through oxidizing gas supply pipe 41 and is fed tothe oxidizing gas supply manifold 8 of cell stack 1. The oxidizing gasthat is supplied flows from oxidizing gas supply manifold 4 into theinlet manifold hole 11 of each cell 2 and passes through oxidizing gaspassage 17. During this time, it reacts with fuel gas through thecathode, polymer electrolyte membrane, and anode and is consumed.Unconsumed oxidizing gas is caused to flow out from outlet manifold hole13 to oxidizing gas discharge manifold 7, and is discharged throughoxidizing gas discharge pipe 42 from stack 1.

Cooling water passes through cooling water supply pipe 30 and is fed tocooling water supply manifold 8 of cell stack 1. The cooling water thatis supplied flows from cooling water supply manifold 8 into the inletmanifold holes 15 and 25 of each cell 2 and passes along cooling waterpassages 19 and 29. During this period, cooling water passes throughcathode separator 10 and anode separator 20, cooling the cathode andanode and collecting heat therefrom. It flows from outlet manifold holes16 and 26 to cooling water discharge manifold 9, and is dischargedthrough cooling water discharge pipe 31 from cell stack 1.

In this process, the fuel gas and oxidizing gas flow through fuel gaspassage 28 and oxidizing gas passage 17, respectively, in a manner thatdoes not run counter to gravity, thereby preventing flooding.

In each of separators 10 and 20, the upstream portions of fuel gaspassage 28 and oxidizing gas passage 17 are positioned in the vicinityof the cooling water inlet, where the relative humidity is the lowest,thereby preventing drying out of the polymer electrolyte membrane.

Implementation Mode 2

FIG. 5 is a view of the rear surface of the anode-side separator of thefuel cell of Implementation Mode 2. FIG. 5 shows parts that areidentical or correspond to parts in FIG. 4.

In the present implementation mode, cooling water supply manifold 8 incell stack 1 of Implementation Mode 1 shown in FIG. 12 has the samecross-sectional shape as the cooling water inlet manifold hole 25A ofthe anode-side separator 20A shown in FIG. 5.

As shown in FIG. 5, in anode-side separator 20A, cooling water inletmanifold hole 25A is divided by a constriction (shown in FIG. 5 asopposed protrusions although other constructive shapes may be employed)32 into a first portion 31 a and a second portion 31 b. Although notshown, the cathode-side separator and MEA cooling water inlet manifoldhole are fashioned with the same shape as cooling water inlet manifoldhole 25A of anode-side separator 20A. First portion 31 a of inletmanifold hole 25A is where cooling water supplied by cooling watersupply pipe 30 to cooling water supply manifold 8 passes, and secondportion 31 b is where cooling water is supplied to cooling water passage29. The remainder of the present implementation mode is identical toImplementation Mode 1.

Referring to FIGS. 12 and 5, in the fuel cell of the presentimplementation mode configured as set forth above, cooling water issupplied to the portion corresponding to first portion 31 a of inletmanifold hole 25A of cooling water supply manifold 8 by cooling watersupply pipe 30. The cooling water that is supplied is distributed toindividual cells 2 while flowing in the direction of stacking of cellstack 1. When there is no constriction 32 in inlet manifold hole 25A,the effect of gravity causes larger quantities of cooling water to tendto flow into the cells that are closer to cooling water supply pipe 30.In the present implementation mode, constriction 32 has the effect ofcausing the cooling water supplied to cooling water inlet manifold hole25A to first fill the upstream side of constriction 32, that is, theinterior of first portion 31 a, before passing through second portion 31b to the cooling water passages 29 of each of cells 2. This permits theuniform distribution of cooling water to both the cell 2 that is theclosest to cooling water supply pipe 30 to the cell 2 that is thefarthest from it. The cross-sectional area in the direction of passageof cooling water of constriction 32 is desirably set to fall within arange of 1 to 10-fold the sum of the sectional areas of each of thepassages of cooling water passage 29. The direction of passage ofcooling water of constriction 32 is the direction indicated by the Xarrow in FIG. 5; that is, the horizontal direction within the plane ofextension of cell 2 (and thus separator 20A).

Implementation Mode 3

FIG. 6 is a rear surface view of the anode-side separator of the fuelcell of Implementation Mode 3 of the present invention. FIG. 6 showsparts that are identical or correspond to parts in FIG. 4.

In the present implementation mode, cooling water supply manifold 8 incell stack 1 of Implementation Mode 1 shown in FIG. 12 has the samecross-sectional shape as cooling water inlet manifold hole 25B ofanode-side separator 20B shown in FIG. 6.

In separator 20B, cooling water inlet manifold hole 25B has a bottomwith two sections: a first portion 41 a with a deep bottom and a secondportion 41 b with a shallow bottom. In other words, inlet manifold hole25B has a step 47 c in the circumferential direction of the bottom ofthe inner circumferential surface, with a first portion 41 a positionedbeneath step 47 c and the second portion 41 b positioned above step 47c. Although not shown, the cooling water inlet manifold holes of the MEAand the cathode-side separator may also be fashioned in the same shapeas cooling water inlet manifold hole 25B of anode-side separator 20B.First portion 41 a of inlet manifold hole 25B is where cooling watersupplied to cooling water supply manifold 8 by cooling water supply pipe30 flows, and second portion 41 b is where cooling water is supplied tocooling water passage 29.

In separator 20B, second portion 41 b for distributing cooling waterfrom cooling water inlet manifold hole 25B to the individual passages isformed at a position that is vertically higher than first portion 41 asupplied with cooling water by cooling water supply pipe 30. Impartingthis shape to cooling water inlet manifold hole 25B causes cooling waterthat has filled first part 41 a on the upstream side of second portion41 b to increase the horizontal flow speed in the plane of extension ofseparator 20B in second part 41 b and causes cooling water to bedistributed to the individual passages while maintaining this flowspeed, further enhancing the uniform distribution of cooling water.When, as in Implementation Mode 2, the configuration consists of only aconstriction 32 on the inlet side of second portion 31 b and the coolingwater flow rate is reduced during partial load operation, the effect ofthe constriction diminishes and the uniform distribution of coolingwater may be compromised. However, in the present implementation mode,since the bottom of second portion 41 b located on the downstream sideis shallower than the bottom of first portion 41 a located on theupstream side, even when the cooling water flow rate is low, the coolingwater supplied by cooling water supply pipe 30 temporarily collects infirst portion 41 a and then flows to second part 41 b communicating tothe individual passages of cooling water passage 29, ensuring uniformdistribution. Further, foreign matter contained in the cooling watersettles in first portion 41 a, preventing it from flowing into coolingwater passages 29 and preventing cooling water blockage by foreignmatter and the like.

EXAMPLES

Examples of the present invention are described below.

Example 1

Platinum particles with an average particle size of about 30 Å werecoated with 25 weight percent of acetylene black carbon powder (DENKABLACK FX-35 made by Denki Kagaku K.K.). This was employed as the cathodecatalyst. Platinum-ruthenium alloy (Pt:Ru=1:1 (by weight)) particleswith an average particle size of about 30 Å were coated with 25 weightpercent of acetylene black carbon powder (DENKA BLACK FX-35 made byDenki Kagaku K.K.). This was employed as the anode catalyst. Toisopropanol dispersions of these catalytic powders were admixed ethylalcohol dispersions of perfluorocarbonsulfonic acid powder (FlemionFSS-1 made by Asahi Glass K.K.) to form pastes. Using these pastes asstarting materials, screen printing was conducted to form electrodecatalyst layers on one side of nonwoven carbon cloth (TGP-H-090 made byTore Kogyo K.K.) 250 ìm in thickness. The quantity of platinum containedin the catalytic layers of the electrodes thus formed was 0.3 mg/cm²,and the quantity of perflurocarbonsulfonic acid was 1.2 mg/cm².

In these electrodes, the configuration of the cathode and anode wasidentical with the exception of the catalytic material. These electrodeswere bonded to both sides of the center portions of a proton-conductingpolymer catalyst film (FAFION 122 made by DuPont of the U.S.) having anarea one size larger than the electrodes by hot pressing the printedcatalyst layers against the catalyst side. Further, the peripheralportion of the polymer electrolyte membrane exposed around theelectrodes was sandwiched between gaskets comprised of sheets offluorine rubber (Afurasu (registered trademark) made by Asahi GlassK.K.) 250 μm in thickness and hot pressed to integrally bond theassembly. This yielded a membrane electrode assembly (MEA). A 30 μm thinfilm of perflurocarbonsulfonic acid was employed as theproton-conducting polymer electrolyte membrane.

The electrically conductive separator with the structure described inImplementation Mode 1 was employed in the present embodiment. Thefigures show a state where a fuel cell, in which this separator isstacked, is positioned in the same manner as in actual operation, withthe upward direction being up with respect to gravity. In thiselectrically conductive separator, gas passages and manifold holes areformed by mechanically processing an isotropic graphite sheet 3 mm inthickness. Gas passages 17 and 28 are 2 mm in groove width and 1 mm indepth, and the passages are spaced 1 mm apart. They are both configuredas two-path passages. With the exception that the cooling water passageshave a channel depth of 0.5 mm, they are identical to the gas passages.The rated operation conditions of this cell are a fuel use rate of 75percent, an oxygen use rate of 40 percent, and a current density of 0.3Å/cm².

The above-described cell comprised of an MEA sandwiched between acathode-side separator and an anode-side separator was stacked 50 cellsdeep. The two separator plates formed cooling water passages betweenadjacent cells. The cell stack was sandwiched between stainless steelend plates via gold-plated copper current-collecting plates andinsulating plates made of polyphenylene sulfide. The two end plates werefastened with fastening rods. The fastening pressure was 10 kgf/cm² ofthe area of the electrodes. During operation, the stacked cells werepositioned so that the portion of the separator shown in the figures asbeing on top was on top.

The fuel cell of the present embodiment thus manufactured was maintainedat 70° C., fuel gas (80 percent hydrogen gas/20 percent carbondioxide/10 ppm carbon monoxide) that had been humidified and heated toimpart a dew point of 70° C. was supplied to the anode and air that hadbeen humidified and heated to impart a dew point of 70° C. was suppliedto the cathode. This fuel cell was varied from a current density of0.075 Å/cm² constituting a low load of 25 percent of rating to a ratedload of 0.3 Å/cm² and the current-voltage characteristics wereevaluated. However, the use rates in the testing were made identical tothose of rated the conditions. The results are given in FIG. 7. FIG. 7also includes the characteristics of a comparative example fuel cell.The comparative example fuel cell had cooling water inlets and outletsthe reverse of Embodiment 1, with gas being humidified to a relativehumidity of 100 percent at the inlet. It will be understood from thefigure that the fuel cell of the present embodiment did not undergoflooding and operated stably even in the vicinity of 0.075 Å/cm² whereflooding occurred and operation was difficult due to a decrease in thegas flow speed in the fuel cell of the comparative example. In thepresent embodiment, the cooling element is located between theanode-side separator and cathode-side separator of adjacent cells.However, the same effect may be achieved by positioning cooling elementsbetween each of multiple cells.

Example 2

In the present embodiment, the separator described in ImplementationMode 2 was employed. The cross-sectional area in the direction ofcooling water passage of the constriction was designed to fall within arange of from 1 to 10-fold the sum of the cross-sectional areas of thecooling water passages in all of the cooling surfaces. Since the totalcross-sectional area of the two cooling water passages was 4 mm² in thepresent embodiment, the cross-sectional area of the construction wasdesigned to fall within a range of 4 to 40 mm².

When operating the fuel cell under the operating conditions described inEmbodiment 1, the voltage of each cell was measured during rated loadoperation. The results are given in FIG. 8. FIG. 8 also gives thevoltages of individual cells of the fuel cell of Embodiment 1. Theconfiguration here is one where the cooling water is supplied from thenumber 1 cell side, passes through the manifold and cooling waterpassages, and is discharged from the number 50 cell side. The fuel cellof Embodiment 1 will be found to have a voltage level that is high onthe cooling water inlet side, decreasing as one approaches the outlet.This is because the flow rate of cooling water is nonuniform, producinghigh and low-temperature cells. By contrast, it will be found that inthe fuel cell of the present embodiment, the cooling water is moreuniformly distributed, the temperature distribution is uniform, and thecell voltage is rendered uniform. FIG. 9 shows comparison resultsfollowing operation of these fuel cells for 1,000 hours. FIG. 9 showsthat in the cell of Embodiment 1, the rate of deterioration of cellvoltage in the vicinity of the cooling water outlet was high, while inthe cell of the present embodiment, no sharp deterioration was observedin any of the cells. Cell voltage deterioration is thought to occurbecause the temperature rises in cells in which the cooling water flowrate decreases, resulting in deterioration due to drying out of theelectrolyte membrane. Accordingly, the improved uniformity of coolingwater distribution in the present embodiment effectively controlleddeterioration of durability.

Example 3

The separator of Implementation Mode 3 was employed in the presentExample. The cross-sectional surface area of the constriction on theinlet side of portion 41 b communicating with the passage of inletmanifold hole 25B was designed by the same method as in Example 2.

This fuel cell was operated at ¼ rated load under the operatingconditions described in Example 1 and the voltage of each cell wasmeasured when the cooling water was diminished to ¼ of the rated flowrate. The results are given in FIG. 10. FIG. 10 also gives the voltagesof the individual cells of the fuel cell described in Example 2. Theconfiguration here is one where cooling water is supplied from thenumber 1 cell side, passes through the manifold and cooling waterpassages and is discharged from the number 50 cell side. FIG. 10 revealsthat both the cells of Example 2 and the present embodiment were capableof stable operation even at ¼ load. The cell of Example 2 underwentdeterioration in uniformity of cooling water distribution when thecooling water flow rate was reduced to ¼ and tended to undergo increasedvariation in voltage between individual cells. By contrast, the cell ofthe present embodiment maintained uniform cell voltage despite thedecrease in the cooling water flow rate. This was thought to haveoccurred because cooling water temporarily collected in the firstportion 41 a on the upstream side in inlet manifold hole 25B, passingvia second portion 41 b on the downstream side to passage 29, improvingthe uniformity of distribution when the cooling water flow was low.

FIG. 11 shows the results of a comparison of voltages between cellsafter operating the cells for 1,000 hours under low load operatingconditions. FIG. 11 reveals that although the cell of Example 2exhibited a somewhat high rate of deterioration of cell voltage on thecooling water outlet side, the cell of the present embodiment exhibiteda uniform decrease in cell voltage. The deterioration in cell voltagewas thought to have occurred because the temperature increased in cellswith a low cooling water flow rate, causing deterioration due to dryingout of the electrolyte membrane. The improved uniformity of distributionof cooling water of the present embodiment was also found to effectivelysuppress deterioration in durability. In particular, in systemsoperating for extended periods at a diminished cooling water flow rateduring low-load operation, the use of the manifold shape of the presentembodiment is effective.

Based on the present invention as set forth above, by causing theoxidizing gas, fuel gas, and cooling water to all flow in a manner notrunning counter to gravity in the separator, it is possible to promotethe smooth discharge of condensation water, achieve stable and efficientoperation without causing flooding during low-load operation, eliminatedrying out of the electrolyte membrane in the gas inlet portion, andimprove durability.

When the cells are stacked, designing a constriction into the coolingwater inlet manifold hole permits improved uniformity of cooling waterdistribution and permits a reduction in the temperature distributionbetween cells, thus suppressing variation in cell voltage. Further,deterioration in durability is reduced since no cells with hightemperatures are produced.

Still further, positioning the connecting member of the communicatingmember for distributing cooling water from the cooling water inletmanifold hole to the various passages in a higher position with regardto gravity than the position at which cooling water is supplied to thecooling water inlet manifold hole ensures uniform distribution andprevents increased voltage variation due to increased temperaturedistribution even when the cooling water flow rate has been diminishedduring low-load operation.

When used in environments where the orientation of the fuel cellassembly may be varied, e.g., in traveling automobiles, it is within theinvention to provide apparatus to maintain the appropriate orientationsuch that the passages previously described do not run counter togravity.

Based on the description set forth above, numerous improvements andother implementation modes of the present invention will be apparent tothose skilled in the art. Accordingly, the above description should beinterpreted only by way of example, and has been given with the objectof providing those skilled in the art with the best modes ofimplementing the present invention. To the extent that the spirit of thepresent invention is not exceeded, the details of these structuresand/or functions may be essentially varied.

In the various embodiments illustrated in the drawings, the orientationof the fuel cell has been denoted as “up” and “down” with the flow ofliquid being from up towards down.

This application is based on Japanese Patent Application No. 2003-179577filed on Jun. 24, 2003, the entire technical contents of which areexpressly incorporated by reference herein.

1. A polymer electrolyte fuel cell equipped with: a cell comprising: amembrane electrode assembly (MEA) comprising a hydrogen ion-conductingpolymer electrolyte membrane and an anode and a cathode sandwiching thepolymer electrolyte membrane; a platelike anode-side separatorpositioned on one side of the MEA so that a front surface thereofcontacts the anode, with fuel gas passages through which fuel gas flowsbeing formed in the front surface; and a platelike cathode-sideseparator positioned on the other side of the MEA so that a frontsurface thereof contacts the cathode, with oxidizing gas passagesthrough which oxidizing gas flows being formed in the front surface; acell stack in which a plurality of said cells is stacked; and a coolingwater flow passage, through which cooling water flows, formed on atleast the rear surface of one from among the anode-side separator andthe cathode-side separator of at least a prescribed cell in said cellstack; where said fuel gas, oxidizing gas, and cooling water flowthrough said fuel gas passage, oxidizing gas passage, and cooling waterpassage, respectively, in a manner not running counter to gravity. 2.The polymer electrolyte fuel cell of claim 1 wherein said fuel gaspassage, oxidizing gas passage, and cooling water passage are eachformed to run horizontally or with a downward gradient in the directionof flow.
 3. The polymer electrolyte fuel cell of claim 2 wherein atleast one from among said fuel gas passage, oxidizing gas passage, andcooling water passage is comprised of horizontal portions and verticalportions.
 4. The polymer electrolyte fuel cell of claim 1 wherein theupstream portion of the oxidizing gas passage is positioned in thevicinity of the inlet of the cooling water passage in the cathode-sideseparator.
 5. The polymer electrolyte fuel cell of claim 1 wherein theupstream portion of the fuel gas passage is positioned in the vicinityof the inlet of the cooling water passage in the anode-side separator.6. The polymer electrolyte fuel cell of claim 1 wherein said coolingwater passage and oxidizing gas passage are formed in said cathode-sideseparator so as to approximately align overall when viewed in thedirection of thickness.
 7. The polymer electrolyte fuel cell of claim 1wherein, in said anode-side separator and said cathode-side separator,the inlet manifold hole supplying cooling water to the cooling waterpassage runs through said separators in the direction of thickness andis provided with a constriction comprised of locally narrowing portionsin the opposing internal circumference surfaces, with a first portionpositioned on one side of the constriction communicating to a coolingwater supply pipe and a second portion positioned on the other side ofthe constriction communicating to the cooling water flow passage.
 8. Thepolymer electrolyte fuel cell of claim 1 wherein, in said anode-sideseparator and said cathode-side separator, an inlet manifold holesupplying cooling water to the cooling water passages is provided so asto run through the separators in the direction of thickness and to havea step running in a circumferential direction on the lower portion ofthe inner circumference surface, with a first portion positioned beneaththe step communicating to a cooling water supply pipe and a secondportion positioned above the step communicating to the cooling waterflow passage.
 9. A method of operating a fuel cell comprised of an MEAhaving a hydrogen ion-conducting polymer electrolyte membrane and ananode and cathode sandwiching the polymer electrolyte membranecomprising: providing an anode-side separator positioned on one side ofthe MEA such that a front surface thereof contains the anode; providingfuel gas passages formed in the front surface; providing a cathode-sideseparator positioned on one side of the MEA such that a front surfacethereof contacts the cathode; providing oxidizing gas passages formed inthe front surface; feeding a moistened fuel gas through said fuel gaspassages; feeding an oxidizing gas through said oxidizing gas passages;reacting said fuel gas and oxidizing gas resulting in the release ofheat; said released heat increasing the temperature of the fuel cell;passing a cooling fluid comprising water through passages formed on atleast the rear surface of one from among the anode-side separation andthe cathode-side separation of said cell to absorb at least part of saidreleased heat and hydrate the electrolyte membrane; said flowing of saidfuel gas and said oxidizing gas being in a direction not counter togravity from an inlet to an outlet of said fuel gas and said oxidizinggas flow through said cell.
 10. The method according to claim 9, whereinsaid flowing comprises flowing said fuel gas in a direction eitherhorizontal or in a downward gradient from an inlet to an outlet of saidfuel gas.
 11. The method according to claim 9 in which the flow of saidoxidizing gas is in a direction either horizontal or in downwardgradient from an inlet to an outlet of said oxidizing gas.
 12. Themethod of claim 11 in which the flow of said oxidizing gas is also in avertically downward direction.
 13. The method of claim 9 in which thefuel gas flows from an inlet proximate a top of said fuel cell to anoutlet proximate to a bottom of the fuel cell.
 14. The method of claim13, wherein the cooling fluid flows from an inlet proximate the top ofsaid fuel cell to an outlet proximate the bottom of the fuel cell. 15.The method of claim 13, wherein the flow of cooling fluid is in adirection countercurrent with the flow of the fuel gas.
 16. The methodof claim 13, wherein the inlet of the cooling fluid is proximate theinlet of the fuel gas.
 17. The method of claim 9, wherein the maintainedfuel gas is moistened to less than 100 percent relative humidity. 18.The method of claim 9, wherein condensation forms in at least one of thefuel gas passages and the cathode gas passages, said method furthercomprising flowing said condensation out of said fuel cell throughpassages which are at least one of horizontal and vertical descending;downwardly descending; downwardly descending and vertically descending;and horizontal, downwardly descending and vertically descending.
 19. Themethod of claim 18, wherein said condensation flows through passageswhich are essentially horizontal and vertically descending.
 20. Themethod of claim 19, wherein said condensation flows through at least twoseparate but parallel passages.
 21. The method of claim 14, wherein aconstriction is present in a flow path of the cooling fluid at aposition intermediate the cooling fluid passage and a cooling fluidsupply manifold.
 22. The method of claim 9, in which the oxidizing gasflows from an inlet proximte a top of said fuel cell to an outletproximate a bottom of the fuel cell.
 23. The method of claim 22, furthercomprising flowing the cooling fluid from an inlet proximate the inletof said oxidizing gas to an outlet proximate a bottom of the fuel cell.24. The method of claim 23, wherein the flows of the oxidizing gas andthe cooling fluid are countercurrent.
 25. The method of claim 9, furthercomprising providing a construction in an inlet for the cooling fluidpassage and flowing the cooling fluid through said constriction.
 26. Themethod of claim 25, wherein the constriction is provided in the form ofa flow passage interrupted by opposed protrusions.
 27. The method ofclaim 25, wherein the constriction is provided in the form of a step ina flow path of the cooling fluid.
 28. The method of claim 9, wherein thecooling fluid flow passage and the oxidizing gas flow passage arealigned throughout as viewed in the direction of thickness of thecathode-side separator.